I got called to the office last semester for having a pic of a deactivated pineapple grenade as my phone's wallpaper. The principal said he could've had me arrested for it.
And then they went through my pictures (their justification for going through my phone was to find out who's it was, as they picked it up in the cafeteria, because I accidently dropped it, even though I fail to see how looking through my pictures would determine who owned the phone), and said that they found porn (which I didn't, and don't deny having on it). But since I'm 18, they couldn't have done anything, other than a strongly-worded encouragement to delete the pics.